BackupPC: How do I run hourly incr backups?

# Minimum period in days between incremental backups (a user requested
# incremental backup will be done anytime on demand).
#
# Typically this is set slightly less than an integer number of days. The
# time taken for the backup, plus the granularity of $Conf{WakeupSchedule}
# will make the actual backup interval a bit longer.
#
#$Conf{IncrPeriod} = 0.97;
[B]$Conf{IncrPeriod} = 0.1;[/B]

I tried setting it to 0.1, but that doesn't seem to be working. How do I run hourly incremental backups? Or every two hours?